1. Field of the Invention
The invention relates to methods and apparatus to facilitate transvaginal endoscopic surgery.
2. Endoscopic Uterine Surgery
Endoscopic surgery is frequently performed on the uterus transvaginally. This anatomic approach requires sufficient dilation of the vaginal canal to allow manipulation of the surgical instruments and to give the surgeon enough visibility to properly guide the endoscope. In an anesthetized patient, a weighted speculum is commonly employed to maintain the desired degree of vaginal dilation, but the speculum occasionally interferes with free movement of the endoscope. Another disadvantage of a weighted speculum is that its presence impedes the collection and accurate measurement of fluid drainage from the vagina.
Fluid drains continuously from the vagina during transvaginal endoscopic surgery because a continuous flow of water-based irrigation fluid passes through the endoscope from an external reservoir. Irrigation fluid flow in the area of surgery removes small pieces of excised tissue and blood, continually clearing the surgeoffs endoscopic view of the operative site(s). Most of the irrigation fluid which enters the uterus through the endoscope is subsequently flushed out through the cervix and vagina by additional irrigation fluid. However, a portion of the entering fluid is absorbed through the endometrium and through parts of the patient's vascular system exposed by the surgery. During relatively prolonged and/or invasive uterine surgery, sufficient fluid may be absorbed to substantially adversely alter the patient's serum electrolyte balance. Because serious electrolyte imbalances may result in seizures, coma or death of the patient, the surgeon must have sufficient warning of impending imbalances to take corrective action. Hence, frequent estimates of serum electrolyte levels may be required during certain endoscopic uterine surgical procedures.
Serum electrolytes are conventionally determined by laboratory analysis of blood samples obtained by venipuncture. Repeated sampling in this manner, however, is disturbing to the patient and unnecessary. A more convenient method for estimating serum electrolyte levels relies on accurate determination of baseline electrolyte concentrations, combined with estimates of the amount of absorbed irrigation fluid.
Estimates of absorbed irrigation fluid, however, are presently relatively inaccurate because of difficulty in monitoring the total amount of fluid which drains from the vagina, as well as that released through use of endoscopic instruments near the vagina. A fraction of the drained and released waste irrigation fluid typically falls on surgical drapes and thence to the operating table or floor, where it is commonly lost without being measured. Because the volume of this lost fraction of waste fluid is generally unknown, the amount of irrigation fluid absorbed by the patient is difficult to estimate accurately during the course of an operation.